Introducing their study, Chen et al. (2016) write that "high-resolution temperature reconstruction for the past 2000 years is imperative for understanding long-term natural climate variations and for estimating anthropogenic influence on the climate system." And, therefore, they developed an even longer April-June 2665-year tree-ring width chronology based on April-June maximum temperatures recorded at four meteorological stations located near Qilian juniper trees growing near the upper tree-line of the Animaqin Mountains on the eastern Tibetan Plateau. And what did they learn by so doing?

As illustrated in the accompanying figure below, the four researchers report that "the warmest period occurred in AD 890-947, that "the coldest period occurred in AD 351-483," that "no obvious warming trend since the industrial revolution was observed," that "the mean of the most recent 50 years was only slightly higher than that of the whole series," and that it "has not yet reached the high values attained earlier."

In addition, Chen et al. note "the results of wavelet analysis showed the occurrence of significant quasi-periodic patterns at a number of occurring periods (2-8 years, 20-30 years, 30-60 years, and 60-130 years," as well as "some long-term periods (more than 200 years)," which they say were "consistent with those associated with ENSO [El Nino Southern Oscillation], PDO [the Pacific Decadal Oscillation], and solar activity."

Last of all, the five researchers report that "the warmest period was from AD 890 to 947, as opposed to the recent period," which finding implies that there has been nothing unusual, unnatural or unprecedented about the Animaqin Mountains' recent thermal history.

Figure 1. The reconstructed temperature series for the Animaqin Mountains on the eastern Tibetan Plateau. Source Chen et al. (2016).